RC3: EXIF Bug(s)

[Mike2005]

1) The exif field "Shutter speed" seems to be miscalculated (e.g. Exposure time 13/10 is not Shutter speed -0.4).

2) More an esthetical issue than a bug: When the focal length is X.0 mm, the zero after the point isn't displayed. For example, it gets displayed as "18." instead of "18.0". Looks a little strange.


XnView 1.82 RC3

[xnview]

1) The exif field "Shutter speed" seems to be miscalculated (e.g. Exposure time 13/10 is not Shutter speed -0.4).

2) More an esthetical issue than a bug: When the focal length is X.0 mm, the zero after the point isn't displayed. For example, it gets displayed as "18." instead of "18.0". Looks a little strange.

Could you send me this picture, please?

[Mike2005]

Hi Pierre,

The 13/10 = -0.4 problem seems to be solved in release 1.82.2.

1) But in most cases XnView is still miscalculating the shutter speed (see example 1: exposure time 1/1250 is not shutter speed 10.3).


Example 1

2) There seem to be some rounding errors (see example 2: exposure time 3/5 vs. shutter speed 0.7).


Example 2

3) I'm not absolutely sure about this, but there also seems to be a rounding error in f-number calculation for raw files. In example 3, XnView is showing f3.9. When I convert this file with a raw converter, I'll get f4.0.


Example 3

4) Example 3 also shows a minor labeling confusion: the german translation for "shutter speed" is "Verschlusszeit" and not "Belichtungszeit".

If you're interested in the sample pictures, I'll mail them.

Regards, Mike

[xnview]

If you're interested in the sample pictures, I'll mail them.

Yes, please sned me samples per email, and tell me your problem...

[Mike2005]

After I exchanged some mails with Pierre, I re-thought about the shutter speed value problem:

(1) According the EXIF specifications (http://www.exif.org/Exif2-2.PDF, Annex C), "shutter speed" is not the same as "exposure time". It is a logarithmic value used for camera internal exposure calculations in the APEX system (http://doug.kerr.home.att.net/pumpkin/APEX.pdf).

Code: Select all

Shutter speed = - ld ( Exposure time )

(2) Most progs including XnView before 1.82 show for the tag "shutter speed" a time value in seconds. This means they recalculate the exposure time from the shutter speed value using an exponential function.
Imho this is useless because the only thing you get is an exposure time which is inexact because of rounding errors (e.g. 1/807 instead of 1/800).

(3) In XnView 1.82 (until 1.82.2), there was a change. "Shutter speed" now showed the logarithmic APEX value.

(4) After my initial posting in this thread (which was wrong, sorry ), XnView 1.82.2 now doesn't any longer show negative values for "shutter speed". If the APEX value would be negative (exposure time > 1), it seems to calculate the exposure time in seconds as decimal number, otherways it shows the logarithmic APEX value. This is kind of confusing. Btw: For Camera raw images, XnView always shows the exposure time and never the APEX value.

If someone thinks this to be only an academic discussion ... he may be right .

[xnview]

After I exchanged some mails with Pierre, I re-thought about the shutter speed value problem:

(1) According the EXIF specifications (http://www.exif.org/Exif2-2.PDF, Annex C), "shutter speed" is not the same as "exposure time". It is a logarithmic value used for camera internal exposure calculations in the APEX system (http://doug.kerr.home.att.net/pumpkin/APEX.pdf).

Code: Select all

Shutter speed = - ld ( Exposure time )

(2) Most progs including XnView before 1.82 show for the tag "shutter speed" a time value in seconds. This means they recalculate the exposure time from the shutter speed value using an exponential function.
Imho this is useless because the only thing you get is an exposure time which is inexact because of rounding errors (e.g. 1/807 instead of 1/800).

(3) In XnView 1.82 (until 1.82.2), there was a change. "Shutter speed" now showed the logarithmic APEX value.

(4) After my initial posting in this thread (which was wrong, sorry ), XnView 1.82.2 now doesn't any longer show negative values for "shutter speed". If the APEX value would be negative (exposure time > 1), it seems to calculate the exposure time in seconds as decimal number, otherways it shows the logarithmic APEX value. This is kind of confusing. Btw: For Camera raw images, XnView always shows the exposure time and never the APEX value.

If someone thinks this to be only an academic discussion ... he may be right .

But like i said to you, in many programs (exifer, exiftools, photoshop 7....), exposure time & shutter speed are shown with same value... So which value is needed? APEX or not...

[Xyzzy]

I'd say APEX, because it is what this field should show. And we also have a field with "interpreted" value, so there is no problem with getting "intuitive" value.
There are a lot of caveats in EXIF tags (especially maker notes), so I think it is best not to overinterpret them. So, generally, we can change format (0.66 instead of 2/3 or 18 instead of 18.000), but the value should not be changed.

X.

[Mike2005]

@xnview:

(1) I see you decided to go for the interpreted value.
But you still use both concepts.
In JPEGs, you use the interpreted value for shutter speed,
in camera raw files (at least .CRW) you use the APEX value.

(2) There's also an error in exposure time calculation for camera raw files as you can see in the screenshot below.
E.g. 1/1250s is not 0.30s. If you're interested, you can download a .CRW file here.



Michael